The present invention relates to load bearing architectural columns and related structures of the type often used in residential (and similar) construction.
The use of columns as supporting structural elements is common throughout history with the most notable and classic styles having been developed in ancient Greece and Rome.
The aesthetic appeal of columns, combined with their structural advantages, makes them a favorite architectural element in residential housing and related structures.
Historically, of course, columns were made of stone or other heavy materials. Indeed, many structures continue to use columns of this type. Although such column materials are structurally sound, in less-demanding applications such as residential construction they can be somewhat impractical.
More recent developments include decorative columns formed from materials such as extruded aluminum formed into hollow columns with sidewalls that support compression loads along the axis of the column. These are, however, still relatively heavy making the columns difficult to transport, manipulate, and fix in a structure. Because the columns are hollow, they have some aesthetically undesirable characteristics such as rattling and offering a hollow sound when struck.
As an alternative, ornamental columns and arch structures for residential and similar structures have been custom fabricated from wood. Other pre-fabricated columns are formed from fiberglass-reinforced plastics. Others are formed from fiber structures with resin infusion. Other columns are made using continuous filament winding processes.
For reasons of cost and availability, the structural (weight-bearing) functions of many residential columns are based upon a four inch by four inch (“4×4”) treated wood post surrounded by a decorative column exterior. Although the appearance of such treated posts is generally aesthetically unacceptable (with the exception of decking and related structures) they have the advantage of relatively low cost and wide ranging availability. Adding the column exterior provides the desired appearance.
Treated wood posts nevertheless are relatively heavy. Being formed of wood, they will almost invariably twist, bow and warp in use. Additionally, the natural expansion and contraction of wood based upon temperature and humidity conditions causes problems in keeping the post adhered to the remainder of the column. Wooden structures are also susceptible to attack from termites, carpenter ants, and fungi.
As a result, if the decorative portion of the column is attached directly to the treated post, the warping and twisting of the treated post will damage the decorative exterior. Thus, the treated post and decorative shell should be spaced from one another. Additionally, the chemical compositions used to treat the wood against rotting or other decomposition tend to bleed from the post and onto the surrounding structure. The wood-preservative compositions can also tend to accelerate the oxidation of metals, and thus can adversely affect any nails, screws or other fasteners used in or near the column.
As another problem, in a post and shell structure the treated post needs to be centered within the decorative portion of the column and avoid touching the PVC shell. As a result, the post's location is often determined by the desired position of the decorative exterior of the column rather than the structural requirements of the end use.
As yet another problem, a 4×4 treated post is typically put into position by being glued to a concrete pad at the bottom and then being toe nailed to the cross beam at the top. A toe-nail is, however, a relatively weak fastening technique. Toe-nailing tends to split and weaken the wood. Toe-nailing is also less exact than other types of connections and will in time allow the column to shift. Because of the angle of the screw or nail, maximum holding strength cannot be achieved. This is less than desirable from a structural standpoint even if consistent with building codes. Over time, the glued and toe-nailed structure will eventually crack and fail.
Additionally, the fibrous nature of wood allows water to wick up from the bottom of the post eventually causing structural failure.